The disclosures of the following priority applications are herein incorporated by reference:
Japanese Patent Application No. 2001-261397 filed Aug. 30, 2001
Japanese Patent Application No. 2002-005869 filed Jan. 15, 2002
1. Field of the Invention
The present invention relates to a shading device that is employed in a lens barrel mounted at a camera or the like and prevents leakage of light and a lens barrel that employs the shading device.
2. Description of the Related Art
Shading devices that prevent light leakage in the related art include the device disclosed in Japanese Laid-open Patent Publication No. H 09-152541. The shading device, achieved by mounting an accordion-folding shading member at two lens groups housed in the lens barrel, prevents leakage of light from occurring between the lens groups. When these lens groups are caused to move relative to each other for focal adjustment or zooming, the accordion-folding member expands/contracts in conformance to the movement of the lens groups.
However, there is a problem in that when the lens groups rotate around the optical axis for focal adjustment or zooming, the accordion-folding member becomes twisted and, for this reason, the two ends of the accordion-folding member cannot be directly secured to the lens groups.
An object of the present invention is to provide a shading device capable of preventing leakage of light with a high degree of reliability during movement of the lens groups and a lens barrel having this shading device.
A shading device according to the present invention, which is employed in a lens barrel having a plurality of lens groups, includes a plurality of substantially tubular shading members provided between a first lens group and a second lens group that move relative to each other along the optical axis and overlap each other along the optical axis so as to allow the shading device to achieve a telescopic function.
It is desirable that the shading members include a first shading member having one end thereof secured to the first lens group, a second shading member having one end thereof secured to the second lens group and at least one middle shading member provided between the first shading member and the second shading member. In addition, retaining portions should be provided at the unsecured end of the first shading member, the unsecured end of the second shading member and the two ends of the middle shading member.
The shading members may each be formed as a tube having a substantially circular-conical shape and, in such a case, the shading members should be arranged so that the vertices of the individual circular cones face the same direction. In this structure, the area over which the internal circumferential surface on the smaller-diameter side of a shading member overlaps the external circumferential surface on the larger-diameter side of an adjacent shading member may function as a retaining portion.
It is desirable that the shading device as a whole achieve a substantially circular-conical tubular form constituted with the plurality of shading members and that the larger-diameter side of the shading device be set either at the first lens group or the second lens group having the larger lens external diameter. Alternately, the smaller-diameter side of the shading device may be set toward the subject along the optical axis.
It is desirable that at least either the first lens group or the second lens group move while rotating around the optical axis and that the plurality of shading members be capable of rotating while sliding against one another.
It is desirable that the internal diameter of the unsecured end of the first shading member be set smaller than the external diameter of the middle shading member at the end overlapping the first shading member and that the external diameter of the unsecured end of the second shading member be set larger than the internal diameter of the middle shading member at the end overlapping the second shading member.
As the distance between the first lens group and the second lens group becomes smaller, the second shading member is inserted further into the middle shading member and the middle shading member is inserted further into the first shading member to contract the shading device, whereas as the distance between the first lens group and the second lens group becomes larger, the second shading member is pulled out of the middle shading member and the middle shading member is pulled out of the first shading member to allow the shading device to expand.
When the distance between the first lens group and the second lens group is at its smallest, the length of the shading device along the optical axis may become substantially equal to the length of one of the shading members along the optical axis.
A shading device according to the present invention, which is employed in a lens barrel having a plurality of lens groups, includes a light leakage preventing member having bellows provided between a first lens group and a second lens group that move relative to each other along the optical axis, and one end of the light leakage preventing member is secured to the first lens group, whereas another end of the light leakage preventing member is allowed to come into contact with the second lens group.
It is desirable that at least either the first lens group or the second lens group move while rotating around the optical axis and that the sliding member be provided at, at least, the other end of the light leakage preventing member or the second lens group in order to reduce the extent of friction occurring at the contact surface where the other end of the light leakage preventing member and the second lens group come into contact with each other.
The first lens group is capable of moving as it rotates around the optical axis during a focusing operation.
It is desirable that the sliding member be provided at the other end of the light leakage preventing member.
The other end of the light leakage preventing member may be allowed to become detached from the second lens group when the bellows are expanded. It is desirable that the length of the light leakage preventing member when the bellows are expanded be equal to or larger than half the maximum distance between the first lens group and the second lens group.
The light leakage preventing member is capable of expanding through a self-restorative power as the distance between the first lens group and the second lens group lengthens.
It is desirable that the first lens group be provided toward the subject along the optical axis.
It is desirable that the shading device further include an air pressure adjustment device that performs an air pressure adjustment for an interior space formed by the first lens group, the second lens group and the light leakage preventing member and the space outside the interior space as the distance between the first lens group and the second lens group increases/decreases while the other end of the light leakage preventing member and the second lens group are in contact with each other.
It is desirable that the air pressure adjustment device be constituted as grooves that are formed at a contact surface where the second lens group comes in contact with the other end of the light leakage preventing member and communicates between the interior space and the exterior space when the other end of the light leakage preventing member and the second lens group are in contact with each other.
A lens barrel according to the present invention includes a first lens group and a second lens group that move relative to each other along the optical axis with at least either of the lens groups allowed to rotate around the optical axis and a shading device provided between the first lens group and the second lens group. The shading device includes a plurality of substantially tubular shading members which overlap one another along the optical axis so as to allow the shading device to achieve a telescopic function.
A lens barrel according to the present invention includes a first lens group and a second lens group that move relative to each other along the optical axis with at least either of the lens groups allowed to rotate around the optical axis and a shading device provided between the first lens group and the second lens group. The shading device includes a light leakage preventing member having bellows, with one end of the light leakage preventing member secured to the first lens group and another end of the light leakage preventing member allowed to come in contact with the second lens group.